Fiber structure

ABSTRACT

Provided is a fabric having a ground weave to which a hygroscopic polymer is fixed, and the fabric generates heat under moisture absorbing conditions and provides a more comfortable feeling to a person by temperature drop in moisture desorption conditions. A fiber structure is prepared by fixing a hygroscopic polymer to fibers of the fabric, and the front layer on the front surface side and the back layer on the back surface side have different fiber densities where the boundary between the front layer and the back layer is on the center line of a cross section of the fiber structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This is the U.S. National Phase application of PCT/JP2013/054834, filedFeb. 26, 2013, which claims priority to Japanese Patent Application No.2012-040816, filed Feb. 28, 2012, the disclosures of each of theseapplications being incorporated herein by reference in their entiretiesfor all purposes.

FIELD OF THE INVENTION

The present invention relates to a fiber structure of which temperaturechanges by moisture absorption and desorption of the structure.

BACKGROUND OF THE INVENTION

Fabrics having heat retaining and generating properties have beenproposed. The fabrics are produced by fixing hygroscopic polymers andgenerate heat when absorbing moisture.

For example, a knitted fabric disclosed in Patent Literature 1comprises, in a layer to come into contact with the skin, syntheticfiber multifilaments having a larger single fiber fineness than that ina layer opposite to the layer to come into contact with the skin and isa fabric having a function of adsorbing a large amount of water.

Patent Literature 2 proposes an interior material having a sheet-likestructure to which highly hygroscopic microparticles are fixed, and thetemperature of the interior material rises by 3° C. or higher when theinterior material absorbs moisture.

In contrast, there has been no study about temperature drop bydischarging water vapor from fabrics or about a woven fabric structureor a knitted fabric structure readily discharging water vapor.

In the field of automobiles, as pure electric vehicles and hybridelectric vehicles have been popularized, there is a demand for savingpower consumption of the vehicles as much as possible and increasingtravel distance and fuel efficiency. A way to achieve such electricpower saving is to elevate the temperature setting of an air-conditionerin summer. In such a circumstance, in order to suppress uncomfortablefeelings caused by an elevation in the temperature setting of anair-conditioner, automobile interior materials are required to have afunction of dropping temperature. Unfortunately, fiber structurescomprising conventional hygroscopic materials have insufficienttemperature drop effect.

PATENT LITERATURE

Patent Literature 1: Japanese Unexamined Patent Application Publication(Kokai) No. 2002-327316

Patent Literature 2: Japanese Unexamined Patent Application Publication(Kokai) No. 2003-96672

SUMMARY OF THE INVENTION

The present invention has an object to provide a fiber structure thatcan more greatly change the surface temperature of a fabric by moistureabsorption or moisture desorption.

The present invention adopts the means below in order to solve theproblems. In order to solve the problems, the present inventioncomprises the aspects below.

[1] A fiber structure prepared by fixing a hygroscopic polymer to fibersof a fabric, a front layer on a front surface side of the fiberstructure and a back layer on a back surface side of the fiber structurehaving different fiber densities, a boundary between the front layer andthe back layer being on a center line of a cross section of the fiberstructure.

[2] The fiber structure according to the above [1], wherein the fabricis in the form of a woven fabric or a knitted fabric, and the fabric hasa ground weave in the back layer side.

[3] The fiber structure according to the above [1] or [2], wherein thehygroscopic polymer is a polymer of one or more monomers selected fromsodium acrylamido-2-propanesulfonate, sodium styrenesulfonate, sodiumisoprenesulfonate, sodium allylsulfonate, and sodium methallylsulfonateor a copolymer of one or more of the monomers and an additional monomerexcept the monomers.

[4] The fiber structure according to any one of the above [1] to [3],wherein the hygroscopic polymer is fixed to the fabric in a fixing ratioof 4 to 20% by mass.

[5] The fiber structure according to any one of the above [1] to [4],wherein the number of cross section fibers contained in the back layerdivided by the number of cross section fibers contained in the frontlayer (the ratio of the numbers of cross section fibers) ranges from 2to 10, where the fiber structure is cut in the direction perpendicularto a weaving or knitting direction of the fiber structure, and thecenter line of the cross section is the boundary between the front layeron the front surface side and the back layer on the back surface side.

[6] The fiber structure according to any one of the above [1] to [5],wherein the fabric has a weave selected from the following groups a toc:

group a: a warp knit that is produced with a knitting machine equippedwith two or more reeds and has a two needle swing weave or a threeneedle swing weave for the back layer;

group b: a weft knit that is produced with an interlock knitting machineand has a patterned weave for the front layer; and

group c: a pile fabric having a ground weave.

[7] A vehicle interior material comprising the fiber structure accordingto any one of the above [1] to [6].

The present invention provides a fiber structure that is in the form ofa woven fabric or a knitted fabric, and the temperature of the fabricgreatly changes by moisture absorption or moisture desorption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional photograph of a fiber structure in Example1.

FIG. 2 is a cross-sectional photograph of a fiber structure in Example2.

FIG. 3 is a cross-sectional photograph of a fiber structure in Example3.

FIG. 4 is a cross-sectional photograph of a fiber structure inComparative Example 1.

FIG. 5 is a cross-sectional photograph of a fiber structure inComparative Example 2.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A fabric of the present invention will be described first. The fabric ofthe present invention may be in any form of a nonwoven fabric, a wovenfabric, and a knitted fabric but is preferably in the forms of a wovenfabric and a knitted fabric.

The fabric preferably has a ground weave, which affects physicalproperties such as breaking strength and tearing strength of the fabric,in the back layer. Such a structure allows the front layer to providecomfortable texture, touch, appearance, and other characteristics of thefabric.

In a fiber structure according to exemplary embodiments of the presentinvention, a front layer on a front surface side of the fiber structureand a back layer on a back surface side of the fiber structure havedifferent fiber densities, and the boundary between the front layer andthe back layer is on the center line of a cross section of the fiberstructure.

The ground weave differs from a pile weave or a patterned weave in wovenfabrics and knitted fabrics and is a weave that greatly affects physicalproperties such as breaking strength and tearing strength of a fabric.The ground weave for a warp knit produced with two or more reeds is atwo needle swing weave or a three needle swing weave. The ground weavefor a weft knit is a weave knitted with an interlock knitting machine.The ground weave for a woven fabric is a weave that fixes pile in awoven fabric having the pile, such as a moquette pile fabric. Inembodiments of the present invention, the ground weave is used as theback layer to come into contact with the skin, and the back layer of thefabric has a high fiber density. As a result, when a liquid containing ahygroscopic polymer or a raw material of a hygroscopic polymer isinfiltrated into fibers by capillarity and the hygroscopic polymer isfixed to the fabric, a larger amount of the hygroscopic polymer can befixed onto the fibers in the back layer than that onto the fibers in thefront layer.

The fibers constituting the back layer preferably have a total finenessranging from 30 to 500 dtex. Fibers having a total fineness of less than30 dtex reduce the mechanical strength of the ground weave, and thus maycause broken thread or other defects when actually used as a vehicleinterior material such as fabrics for seats. Fibers having a totalfineness of more than 500 dtex excessively increase the amount of thefibers per unit volume of the back layer side, and thus are likely tomake a whole fabric have a hard texture when a hygroscopic polymer isfixed to such a fabric. The single fiber fineness is preferably 0.8 to 5dtex.

The fibers constituting the back layer preferably have a strength of 2.0cN/dtex or more, more preferably 2.5 cN/dtex or more. In order to fix anappropriate amount of the hygroscopic polymer, the single fiber finenessis 0.5 to 5.0 dtex, preferably not less than 0.8 dtex and 5.0 dtex orless. These fibers are preferably in the forms of multifilaments andspun yarn.

In a preferred embodiment of the present invention, the number of crosssection fibers contained in the back layer divided by the number ofcross section fibers contained in the front layer (the ratio of thenumbers of cross section fibers) preferably ranges from 2 to 10, wherethe fiber structure is cut in the direction perpendicular to a weavingor knitting direction of the fiber structure, and the center line of thecross section is the boundary between the front layer on the frontsurface side (the side not to come into contact with the skin) and theback layer on the back surface side (the side to come into contact withthe skin). The ratio of the numbers of cross section fibers is morepreferably 2.5 or more, even more preferably 3.0 or more and is morepreferably 9.5 or less, even more preferably 9.0 or less.

The calculation method of the ratio of the numbers of cross sectionfibers will be described with reference to FIGS. 1 to 5.

FIGS. 1 to 5 are cross-sectional photographs of fiber structures eachcut in the direction perpendicular to a weaving or knitting direction ofthe fiber structure. The cross section of the fiber structure is dividedalong the center line 1 into a side on the front surface 2 and anotherside on the back surface 3. An area from the center line 1 to the frontsurface 2 is regarded as a front layer, and another area from the centerline 1 to the back surface 3 is regarded as a back layer. The number offibers contained in each layer is counted as the number of cross sectionfibers in a corresponding layer.

A fiber structure having a ratio of the numbers of cross section fibersranging from 2 to 10 lowers the relative humidity in an environment andhas a much lower temperature than an environmental temperature. Theinventors of the present invention suppose that the reason is as below.

For the fixation of a hygroscopic polymer to a fabric, to a fabriccontaining a larger number of fibers per unit volume, a larger amount ofthe hygroscopic polymer is fixed among the fibers. Thus, in a fabricthat comprises the back layer containing a larger number of crosssection fibers than the number of cross section fibers contained in thefront layer, a larger amount of the hygroscopic polymer is present inthe back layer than in the front layer. The back layer, which contains alarger amount of the hygroscopic polymer, discharges a larger amount ofwater vapor. The water vapor discharged from the hygroscopic polymer inthe back layer is discharged from the surface of the back layer and alsopasses among the fibers of the fabric. The front layer contains asmaller number of the fibers and a larger space than those in the backlayer. This structure allows the water vapor to readily pass through thefront layer, and thus the water vapor is readily discharged from thesurface of the front layer into air. The water vapor reached form theback layer to the front layer is discharged from the surface of thefront layer into air. This phenomenon lowers the humidity in the fabric,and the heat of vaporization of the water vapor discharged into to airlowers the temperature of the fabric.

In a fabric having a ratio of the numbers of cross section fibers ofabout 1, the amount of the fixed polymer in the front layer issubstantially equal to that of the fixed polymer in the back layer. Thisstructure reduces the difference in discharge amount of water vaporbetween the back layer and the front layer and also reduces thedifference in volume of space, through which water vapor passes, betweenthe back layer and the front layer, and thus the water vapor dischargedfrom the back layer is unlikely to vaporize from the surface of thefront layer. In addition, the water vapor supplied from the back layeris absorbed by the polymer in the front layer, and thus the temperatureof the fabric is unlikely to drop.

A fabric having an excessively large ratio of the numbers of crosssection fibers disadvantageously reduces the heat of vaporization ofwater vapor discharged through the front layer into air, and thus thetemperature of the fabric is unlikely to drop. For the reasons above,the ratio of the numbers of cross section fibers (the number of crosssection fibers contained in the back layer/the number of cross sectionfibers contained in the front layer) is preferably 2 to 10. The ratio ofthe numbers of cross section fibers is more preferably 2.5 or more, evenmore preferably 3.0 or more and is more preferably 9.5 or less, evenmore preferably 9.0 or less.

In an embodiment of the fiber structure of the present invention, theweave is one selected from the groups a to c. Also in the fiberstructure, the front layer on the front surface side and the back layeron the back surface side have different fiber densities, where theboundary between the front layer and the back layer is on the centerline of the cross section of the fiber structure.

Group a: a warp knit that is produced with a knitting machine equippedwith two or more reeds and has a two needle swing weave or a threeneedle swing weave for the back layer.

Group b: a weft knit that is produced with an interlock knitting machineand has a patterned weave for the front layer.

Group c: a pile fabric having a ground weave.

The fiber structure also preferably has a ratio of the numbers of crosssection fibers of 2 to 10. The ratio of the numbers of cross sectionfibers is more preferably 2.5 or more, even more preferably 3.0 or moreand is more preferably 9.5 or less, even more preferably 9.0 or less.The fiber structure also has a much lower temperature than anenvironmental temperature due to a reduction in relative humidity in anenvironment. The reason is the same as the above.

The group a is preferably a warp knit that is produced with a knittingmachine equipped with two or more reeds and has a two needle swing weaveor a three needle swing weave as the ground weave to be the back layer.Examples of the ground weave for the two needle swing weave include1-0/2-3, 2-3/1-0, 0-1/3-2, and 3-2/0-1. Examples of the ground weave forthe three needle swing weave include 1-0/3-4, 3-4/1-0, 0-1/4-3, and0-1/3-4. The ground weave containing at least one or more of the weavesmay be combined with other weaves. The front layer constituting thegroup a may have a one to three needle swing weave, an atlas weave, andother derivative weave, and a weave without threads in which no needleis threaded is also preferred.

The group b is a weft knit that is produced with an interlock knittingmachine and has a patterned weave for the front layer. The ground weaveconstituting the back layer is preferably a tight weave such as a plainknitting weave and a rib knitting weave, and the front layer of the weftknit preferably has a patterned weave as a little loose weave.

The group c is a pile fabric having a ground weave and is preferably amoquette pile fabric comprising rayon fibers in the ground weave and avelvet fabric as a double-woven fabric.

The fabric having the fiber structure of the present inventionpreferably has a surface temperature drop of 1.5° C. to 4° C. when anair-conditioner is operated in an atmosphere at 40° C. and a relativehumidity of 80%, which should be the atmosphere in a car in summer, andthe temperature and humidity conditions are changed from the atmospherecondition to an atmosphere at 35° C. and a relative humidity of 70%within 10 minutes. When the temperature and humidity conditions arechanged from an atmosphere at 40° C. and a relative humidity of 80% toan atmosphere at 35° C. and a relative humidity of 70% within 10minutes, the fiber structure of the present invention to which ahygroscopic polymer is fixed preferably has a surface temperature 1.5°C. to 4.0° C. lower than that of a fiber structure to which nohygroscopic polymer is fixed. The lower limit is more preferably 1.7° C.or more, even more preferably 1.9° C. or more.

The hygroscopic polymer fixed onto fibers of the fabric of the presentinvention preferably has an increase in mass by moisture absorption(hereinafter called moisture absorption ratio) of 10 to 75%, morepreferably 15% or more, even more preferably 20% or more when thetemperature and humidity conditions are changed from an atmosphere at20° C. and a relative humidity of 65% to an atmosphere at 30° C. and arelative humidity of 90%, in terms of hygroscopic properties. Themoisture absorption ratio is more preferably 70% or less, even morepreferably 65% or less. The hygroscopic polymer satisfying suchhygroscopic properties is preferably a polymer of a monomer selectedfrom vinyl group-containing monomers having, as a functional group, asulfo group, a carboxy group, a hydroxy group, an amido group, or alkalimetal salts (preferably a sodium salt) of them or a copolymer containingat least one or more of such monomers. Examples of the polymer having asulfo group preferably include poly(sodiumacrylamido-2-propanesulfonate), poly(sodium styrenesulfonate),poly(sodium isoprenesulfonate), poly(sodium allylsulfonate), andpoly(sodium methallylsulfonate). Examples of the polymer having acarboxy group preferably include poly(sodium acrylate). Examples of thepolymer having a hydroxy group preferably include polyethylene glycoland polyvinyl alcohol. Examples of the polymer having an amido grouppreferably include poly(N-methylolacrylamide) and polyacrylamide. Amongthese hygroscopic monomers, sodium 2-acrylamido-2-methylsulfonate isparticularly preferred in terms of high hygroscopicity.

In addition to these polymers, a copolymer containing additional monomerunits may be used.

In the present invention, in order to improve the fixing properties ofthe hygroscopic polymer to fibers, a cross-linking agent is preferablyused to make the hygroscopic polymer have a cross-linked structure.Examples of the cross-linking agent include polyfunctional epoxycompounds, polyfunctional isocyanate compounds, urea resins, melamineresins, and compounds having at least two polymerizable double bonds.

Examples of the compound having polymerizable double bonds includecompounds prepared by esterifying terminal hydroxy groups ofpolyethylene glycols (for example, having a number average repeat unitof 250) with (meth)acrylic acid. For example, a compound prepared byesterifying a polyethylene glycol having an average repeat of ethyleneoxide of 9 to 23 with two methacrylic acids can be used.

The monomers can be polymerized on fibers constituting the fabric toyield the hygroscopic polymer. The monomer to yield the hygroscopicpolymer and, as necessary, a polymerization initiator can be infiltratedamong fibers constituting the fabric. As necessary, a cross-linkingagent may also be infiltrated. Examples of the polymerization initiatorpreferably include inorganic polymerization initiators such as ammoniumpersulfate, potassium persulfate, and hydrogen peroxide and organicpolymerization initiators such as2,2′-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis(N,N-dimethylene isobutylamidine)dihydrochloride, and2-(carbamolyazo)isobutyronitrile.

As for the method for fixing the hygroscopic polymer to fibers, atreatment liquid containing a monomer, a cross-linking agent (asnecessary), a polymerization initiator (as necessary), and a solvent ora dispersion medium is applied to fibers by padding and then the fibersare heated and dried. Subsequently, the fibers are maintained under ahigh temperature condition with steam or a similar means, thus themonomer and the like are polymerized, and the resulting hygroscopicpolymer is fixed onto the fiber surface. Another method for fixing thehygroscopic polymer to fibers is exemplified by a method of impregnatinga fabric with a solution of a polymer such as poly(sodiumacrylamido-2-propanesulfonate), sodium styrenesulfonate, sodiumisoprenesulfonate, sodium allylsulfonate, and sodium methallylsulfonateand drying the fabric.

In the padding, the treatment liquid for polymerization preferably has aconcentration of monomer to yield the hygroscopic polymer of 20 to 150g/L. For the polymerization with a cross-linking agent, the treatmentliquid preferably has a cross-linking agent concentration of 20 to 150g/L. For the polymerization with a polymerization initiator, thetreatment liquid preferably has a polymerization initiator concentrationof 1 to 10 g/L, more preferably 3 g/L or more, even more preferably 5g/L or more.

For the treatment with a solution of the hygroscopic polymer, thepolymer solution preferably has a concentration of 20 to 150 g/L. Ineach case of polymerization and using a polymer solution, a treatmentliquid having a low concentration results in a reduction in amount ofthe hygroscopic polymer fixed, and this deteriorates coolingperformance. A treatment liquid having a high concentration causes thehygroscopic polymer to be fixed in an excess amount, and this hardensthe texture of the fiber structure.

For the heat treatment, in order to maintain the activity of thepolymerization initiator, a normal-pressure steamer or a high-pressuresteamer is preferably used, and the temperature for the steam treatmentis preferably 80° C. to 170° C.

The heat treatment time is arbitrary and is preferably 5 minutes to 15minutes. The heat treatment time is more preferably 6 to 15 minutes,even more preferably 7 to 15 minutes. The steam pressure is arbitraryand is preferably in a range from 0.09 to 0.50 MPa in order toaccelerate polymerization.

The processing method for fixing, the hygroscopic polymer to fibers ofthe fabric is preferably padding, spraying, and roll coating and isspecifically preferably padding capable of infiltrating an agent intothe fabric.

The hygroscopic polymer is preferably fixed to fibers of the fabric in afixing ratio of 4 to 20% by mass relative to the fabric. A fabriccontaining fibers to which the hygroscopic polymer is fixed in a ratioof less than 4% by mass obtains insufficient hygroscopic properties andthus fails to achieve a large temperature change. A fabric containingfibers to which the hygroscopic polymer is fixed in a ratio of more than20% by mass gives the impression of hard texture. The fixing ratio ofthe hygroscopic polymer to fibers of the fabric is more preferably 5 to18% by mass.

Examples of the fibers constituting the fabric of the present inventioninclude synthetic fibers such as polyester fibers and polyamide fibers,natural fibers such as cotton, and rayon, and these fibers may be usedsingly or as a mixture of two or more of them. From the viewpoint of thereduction in consumption of oil resources, the fibers used arepreferably biomass fibers formed of materials derived from plants, suchas polyethylene terephthalate fibers, polytrimethylene terephthalatefibers, polyamide fibers, and polylactic acid fibers. In particular, thepolytrimethylene terephthalate fibers provide good texture, touch, and acomfortable feeling for sitting due to a low Young's modulus and thusare specifically preferably used. The polylactic acid fibers can beproduced from 100% plant materials, are most contributable fibers to thereduction in consumption of oil resources, and thus are preferred.

The fibers are used in the forms of multifilaments, spun yarns, and thelike. For fibers required to achieve fabric strength or abrasionresistance, the multifilaments are preferred. The preferred totalfineness and single fiber fineness of the biomass fibers are asdescribed in paragraph

The fibers may contain dulling agents such as titanium oxide powder,dyes, pigments, flame retardants, moisture absorbents, heat stabilizers,ultraviolet absorbers, antimicrobial agents, fungicides, deodorants, andother additives as long as the effect of the invention is not impaired.

The light fastness of the fiber structure of the present invention ispreferably the fourth or higher class. When the light fastness of afiber structure is lower than the fourth class, which is determined onthe basis of the grey scale for color change after irradiation with afade meter at 83° C. for 200 hours, the fiber structure causes colorfading or other defects when used for car seats.

The fiber structure of the present invention is preferably used forclothing such as underwear, sportswear, and shirts; interior goods suchas chair upholstery; and vehicle interior materials. The fiber structureparticularly preferably used for vehicle interior materials,specifically for seats. The fiber structure used for seats is preferablyused for main materials, frames, back linings, headrests, seat covers,headrest covers, and other parts.

EXAMPLES

The present invention will now be described in further detail withreference to examples. The present invention is not limited to thefollowing examples, and various modifications and changes may be madewithout departing from the technical scope of the present invention.Each evaluation in the following examples and comparative examples iscarried out by the methods below.

Measurement Method

(1) Tensile Strength (cN/Dtex) and Elongation (%)

The tensile strength (cN/dtex) and the elongation (%) of a thread weredetermined under the constant-rate extension conditions in accordancewith JIS L 1013 (8.5.1) (2010) with TENSILON (registered trademark)UCT-100 manufactured by ORIENTEC Co, Ltd. For the measurement, thesample length was 200 mm, and the tensile speed was 200 m/min. Thetensile strength was determined by dividing a maximum strength on astress-strain curve by a total fineness, and the elongation wasdetermined as an elongation at the maximum strength on the stress-straincurve.

(2) Weight Per Unit Area (g/m²)

In accordance with the method specified in JIS L 1096 (8.4.2) (2010),the weight unit area (g/m²) of a fabric was determined.

(3) Fixing Ratio of Hygroscopic Polymer

From a fabric to which no hygroscopic polymer was fixed, a square samplehaving a size of 30 cm×30 cm was prepared. The sample was left in aconstant temperature and humidity room controlled at a temperature of24° C. and a relative humidity of 60% for 24 hours, and the fabricweight (g) before the treatment (before the fixation of a hygroscopicpolymer) was determined. The fabric weight (g) after the treatment offixing a hygroscopic polymer was then determined under the same constanttemperature and humidity condition as that for the fabric before thetreatment. The fixing ratio of the hygroscopic polymer was calculated inaccordance with the following equation:

Fixing ratio of hygroscopic polymer (%)−[fabric weight after treatment(g)−fabric weight before treatment (g)]/fabric weight before treatment(g)×100

(4) Moisture Absorption Ratio of Fabric (%)

From a fabric before the treatment (before the fixation of a hygroscopicpolymer), about 1.0 g of sample was prepared. The sample was dried in ahot-air drier at 105° C. for 24 hours and then weighed (W1). Next, thesample was left in a thermo-hygrostat controlled at 20° C. and arelative humidity of 65% for 24 hours and then was weighed (W2).Subsequently, the sample was left in a thermo-hygrostat controlled at30° C. and a relative humidity of 90% for 24 hours and then was weighed(W3). From the test results, the moisture absorption ratio of the fabricwas calculated in accordance with the following equation:

Moisture absorption ratio of fabric (%)=[(W3−W1)/W1−(W2−W1)/W1]×100

(5) Moisture Absorption Ratio of Hygroscopic Polymer

The moisture absorption ratio of a fabric after the treatment (after thefixation of a hygroscopic polymer) was calculated from W1, W2, and W3under the same conditions as in paragraph [0047]. On the basis of themoisture absorption ratio of the fabric after the treatment, themoisture absorption ratio of the fabric before the treatment calculatedin paragraph [0047], and the fixing ratio of the hygroscopic polymercalculated in paragraph [0046], the moisture-absorption ratio of thehygroscopic polymer was calculated in accordance with the followingequation:

Moisture absorption ratio of hygroscopic polymer (%)−(moistureabsorption ratio of fabric after treatment−moisture absorption ratio offabric before treatment)×100/fixing ratio of hygroscopic polymer

(6) Ratio of the Numbers of Cross Section Fibers

A fabric was cut in the direction perpendicular to a weaving or knittingdirection. The cut sample was subjected to metal deposition with a metaldeposition apparatus (trade name: E1010) manufactured by Hitachi, Ltd.The sample was then installed in a scanning electron microscope (tradename: S-3500) manufactured by Hitachi, Ltd. and photographed at amagnification of 30 to 100. As shown in FIG. 1 to FIG. 5, the crosssection in each micrograph was divided along the center line 1 into aside on the front surface 2 and another side on the back surface 3. Eachnumber of fibers contained in a front layer from the center line 1 tothe front surface 2 and in a back layer from the center line 1 to theback surface 3 was counted as the number of cross section fibers. Theequation for calculating the ratio of the numbers of cross sectionfibers is shown below.

The ratio of the numbers of cross section fibers=(the number of crosssection fibers contained in the back layer)/(the number of cross sectionfibers contained in the front layer)

(7) Surface Temperature Drop of Fabric

From each of a fabric (A) after the fixation of a hygroscopic polymerand a fabric (B) before the fixation of the hygroscopic polymer, asquare sample having a size of 25 cm×25 cm was prepared. The sample washung in a constant temperature and humidity room controlled at atemperature of 40° C. and a relative humidity of 80% and left for 3hours. The temperature and humidity conditions in the constanttemperature and humidity room were then changed to 35° C. and a relativehumidity of 70%. When a hygrothermograph in the constant temperature andhumidity room indicated 35° C. and a relative humidity of 70%, eachsurface temperature of the fabric (A) and the fabric (B) was determinedwith a thermographic camera (manufactured by NEC Avio InfraredTechnologies Co., Ltd., model: TH7102MX) installed in the constanttemperature and humidity room. The surface temperature drop of thefabric was calculated in accordance with the following equation:

Surface temperature drop of fabric=surface temperature of (B)−surfacetemperature of (A)

(8) Coolness During Sitting

The fabric of the present invention was bonded to a car seat so that thefront surface will come into contact with a person. The car seat wasplaced in a constant temperature and humidity room controlled at 40° C.and a relative humidity of 80%, which should be the atmosphere in a carin summer. A test subject sit on the seat for 5 minutes. The temperatureand humidity conditions were then changed to 25° C. and a relativehumidity of 40%. The test subject sit for another 3 minutes and carriedout a sensory evaluation of the coolness of the seat surface aftersitting. Ten test subjects evaluated the coolness. A sample evaluated tohave coolness by eight or more test subjects is indicated by “verygood,” a sample evaluated to have coolness by four to seven testsubjects is indicated by “good,” and a sample evaluated to have coolnessby three or less test subjects is indicated by “poor.”

(9) Texture

The fabric of the present invention was used, and ten panelistsevaluated the sense of touch of the fabric. The total score from therespective panelists gives a comprehensive evaluation.

Evaluation Standards

Score 3: A soft touch fabric having high surface smoothness.

Score 2: A fabric having average softness and average surfacesmoothness.

Score 1: A fabric having rough, hard feeling and a rough surface.

Comprehensive Evaluation

Very good: 25 to 30 points

Good: 17 to 24 points

Poor: 10 to 16 points

(10) Light Fastness

A fabric was irradiated with an ultraviolet autofade meter (manufacturedby Suga Test Instruments Co., Ltd., model: U48AUHB) for 200 hours undera condition at a black-panel temperature of 83° C., and then the changein color was classified into the first to fifth classes using a greyscale for color change in accordance with JIS L 0804 (2010).

Reference Example 1 Core-Sheath Composite Drawn Yarn

Core-sheath composite drawn yarn with 84T48F was produced frompolyethylene terephthalate (PET) as the core and polytrimethyleneterephthalate (PTT) as the sheath at a mass ratio of 3:7. Thecore-sheath composite drawn yarn was specifically produced as below.

The materials were supplied into a melt spinning machine at the ratioand processed in a spinneret into a core-sheath structure having asingle core. The composite was spun at a spinning temperature of 280° C.The spun yarn was preheated at a rotation speed of the first roll of2,700 m/min and a roll temperature of 40° C., then drawn with heat at arotation speed of the second roll of 4,050 m/min and a roll temperatureof 150° C., and wound up at a winding speed of 3,700 m/min, yieldingcore-sheath composite drawn yarn with 84 dtex-48 f (filament). Thecore-sheath composite drawn yarn had a tensile strength of 3.3 cN/dtexand an elongation of 45%.

Reference Example 2 Polyethylene Terephthalate False-Twisted Yarn

Production methods of polyethylene terephthalate false-twisted yarn with84T36F and polyethylene terephthalate false-twisted yarn with 167T48Fwill be described. Melt spinning was carried out at a spinningtemperature of 284° C. and a spinning speed of 3,000 m/min using aspinneret having a size and a shape suitable for each false-twistedyarn, and the resulting undrawn yarn was wound. Next, false twisting wasperformed at a first heater (noncontact type) temperature of 230° C., anoverfeed ratio of 0.9, a second heater (noncontact type) temperature of200° C., a draw ratio of 1.69, and a machining speed of 600 m/min,yielding polyethylene terephthalate false-twisted yarn with 84 dtex-36 f(filament) and polyethylene terephthalate false-twisted yarn with 167dtex-48 f (filament). The polyethylene terephthalate false-twisted yarnwith 84T36F had a tensile strength of 3.6 cN/dtex and an elongation of23%, and the polyethylene terephthalate false-twisted yarn with 167T48Fhad a tensile strength of 4.0 cN/dtex and an elongation of 22%.

Reference Example 3 Polyethylene Terephthalate Drawn Yarn

A production method of polyethylene terephthalate drawn yarn with 84T48F(84 dtex-48 f (filament)) will be described. Melt spinning was carriedout at a spinning temperature of 290° C. and a spinning speed of 1,500m/min, and the resulting undrawn yarn was wound. Next, the undrawn yarnwas drawn with a drawing machine at a preheat roller temperature of 90°C., a heat treatment roller temperature of 150° C., a draw ratio of3.01, and a machining speed of 970 m/min, yielding polyethyleneterephthalate drawn yarn with 84 dtex-48 f. The drawn yarn had a tensilestrength of 4.0 cN/dtex and an elongation of 35%.

Example 1

A 28-gauge tricot machine was used. With four reeds, the core-sheathcomposite drawn yarn with 84 dtex-48 f (filament) of Reference Example 1was supplied to L1 (for a ground weave) in a full set threadarrangement, the polyethylene terephthalate false-twisted yarn with 84dtex-36 f (filament) of Reference Example 2 was supplied to L2 (for aground weave) in a full set thread arrangement, the core-sheathcomposite drawn yarn with 84 dtex-48 f (filament) of Reference Example 1was supplied to L3 and L4 in a thread arrangement in which a thread isalternately pushed in and pulled out, and the yarns were knitted at acourse density on the machine of 42 C/2.54 cm to prepare a gray fabricin the form of weave 1.

Weave 1, Weave of Group a

L1: 84 dtex-48 f (PET/PTT core-sheath composite drawn yarn), 1-2/1-0(threading: full set)

L2: 84 dtex-36 f (PET false-twisted yarn), 3-4/1-0 (threading: full set)

L3: 84 dtex-48 f (PET/PTT core-sheath composite drawn yarn), 2-3/2-11-0/1-2 (threading: a thread is alternately pushed in and pulled out)

L4: 84 dtex-48 f (PET/PTT core-sheath composite drawn yarn), 1-0/1-22-3/2-1 (threading: a thread is alternately pushed in and pulled out)

The warp knitted fabric obtained was dyed using a jet dyeing machinewith 0.24% owf “Dianix” (registered trademark, hereinafter the sameapplies) KIS-U, 0.11% owf “Dianix” AM-2R, and 0.24% owf “Dianix” GL-FSas dyes and with 1% owf fast-P (trade name) manufactured by Ciba as alight stabilizer while the temperature was increased from roomtemperature to a dyeing temperature of 130° C. at a temperature increaserate of 1° C. and maintained at a dyeing temperature of 130° C. for 25minutes.

The warp knitted fabric dyed as above was next immersed in a treatmentliquid prepared in accordance with the formulation 1 to infiltrate ahygroscopic polymer. The fabric was then squeezed with a mangle so as togive a pick up ratio of 90% and dried in a dryer at 120° C. for 2minutes.

Formulation 1

-   -   Sodium 2-acrylamido-2-methylpropane sulfonate (trade name:        Gracet T505, manufacturer: Hokko Chemicals Co., Ltd.): 120 g/L    -   A dimethacrylate of “polyethylene glycol having a number average        degree of polymerization of 23” (trade name: Gracet T303,        manufacturer: Hokko Chemicals Co., Ltd.) as a cross-linking        agent: 120 g/L    -   Ammonium persulfate (manufacturer: Nacalai Tesque) as a        polymerization initiator: 5 g/L    -   Water

After the warp knitted fabric dyed was impregnated with the hygroscopicpolymer and then dried as above, the fabric was treated with anormal-pressure steamer at 105° C. for 10 minutes, then washed with hotwater, and dried. Next, the dried fabric was further dried in a dryer at160° C. for 1 minute, giving a fiber structure of Example 1 having aweight per unit area of 310 g/m², a fixing ratio of the hygroscopicpolymer of 7.3%, a moisture absorption ratio of the fabric of 2.4%, anda moisture absorption ratio of the hygroscopic polymer of 32.8%.

The fiber structure was cut in a direction perpendicular to the knittingdirection, and the cross-section was observed under an electronmicroscope. FIG. 1 is the electron micrograph (×50). The observationresult indicated that the number of cross section fibers contained inthe front layer was 235, the number of cross section fibers contained inthe back layer was 850, and the ratio of the numbers of cross sectionfibers was 3.62. The result also revealed that the hygroscopic polymerwas fixed onto the fibers of the knitted fabric.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 2.1° C., the coolness during sitting was“very good”, the texture was “very good”, the light fastness was class4, and the fabric provided a highly comfortable feeling when a personsit.

Example 2

A 28-gauge tricot machine and four reeds were used, the polyethyleneterephthalate false-twisted yarn with 167 dtex-48 f (filament) ofReference Example 2 was supplied to L1 (ground weave) in a full setthread arrangement, the core-sheath composite drawn yarn with 84 dtex-48f (filament) of Reference Example 1 was supplied to L2 and L3 in athread arrangement in which a thread is alternately pushed in and pulledout, and the yarns were knitted at a course density on the machine of 50C/2.54 cm to prepare a knitted fabric in the form of weave 2.

Weave 2, Weave of Group a

L1: 167 dtex-48 f (PET false-twisted yarn), 1-0/3-4 (threading: fullset)

L2: 84 dtex-48 f (PET/PTT core-sheath composite drawn yarn), 2-3/2-11-0/1-2 (threading: a thread is alternately pushed in and pulled out)

L3: 84 dtex-48 f (PET/PTT core-sheath composite drawn yarn), 1-0/1-22-3/2-1 (threading: a thread is alternately pushed in and pulled out)

The knitted fabric was then dyed in the same manner as in Example 1, anda hygroscopic polymer was fixed onto the fabric, giving a fiberstructure of Example 2 having a weight per unit area of 275 g/m², afixing ratio of the hygroscopic polymer of 12.3%, a moisture absorptionratio of the fabric of 3.0%, and a moisture absorption ratio of thehygroscopic polymer of 24.3%.

The fiber structure was cut in a direction perpendicular to the knittingdirection, and the cross-section was observed under an electronmicroscope. FIG. 2 is the electron micrograph (×100). The observationresult indicated that the number of cross section fibers contained inthe front layer was 121, the number of cross section fibers contained inthe back layer was 485, and the ratio of the numbers of cross sectionfibers was 4.01. The result also revealed that a large amount of thehygroscopic polymer was fixed to the ground weave of the knitted fabric.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 1.9° C., the coolness during sitting was“very good”, the texture was “very good”, the light fastness was class4, and the fabric provided a highly comfortable feeling when a personsit.

Example 3

A 28-gauge tricot machine and three reeds were used, the core-sheathcomposite drawn yarn with 84 dtex-48 f (filament) of Reference Example 1was supplied to L1 (ground weave) and L2 (ground weave) in a full setthread arrangement, the polyethylene terephthalate false-twisted yarnwith 84 dtex-36 f (filament) of Reference Example 2 was supplied to L3in a full set thread arrangement, and the yarns were knitted at a coursedensity on the machine of 64 C/2.54 cm to prepare a gray fabric in theform of weave 3.

Weave 3, Weave of Group a

L1: 84 dtex-48 f (PET/PTT core-sheath composite drawn yarn), 2-3/1-0(threading: full set)

L2: 84 dtex-48 f (PET/PTT core-sheath composite drawn yarn), 1-0/1-2(threading: full set)

L3: 84 dtex-36 f (PET false-twisted yarn), 1-0/3-4 (threading: full set)

Next, the knitted fabric was dyed in the same manner as in Example 1 andthen was raised with a raising machine. A hygroscopic polymer was fixedto the raised fabric in the same manner as in Example 1, giving a fiberstructure of Example 3 having a weight per unit area of 330 g/m², afixing ratio of the hygroscopic polymer of 12.5%, a moisture absorptionratio of the fabric of 3.0%, and a moisture absorption ratio of thehygroscopic polymer of 24.0%.

The fiber structure was cut in a direction perpendicular to the knittingdirection, and the cross-section was observed under an electronmicroscope. FIG. 3 is the electron micrograph (×50). The observationresult indicated that the number of cross section fibers contained inthe front layer was 220, the number of cross section fibers contained inthe back layer was 1,380, and the ratio of the numbers of cross sectionfibers was 6.27. The result also revealed that the hygroscopic polymerwas fixed to the ground weave of the knitted fabric.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 2.3° C., the coolness during sitting was“very good”, the texture was “very good”, the light fastness was class4, and the fabric provided a highly comfortable feeling when a personsit.

Example 4

A 28-gauge tricot machine and four reeds were used to prepare a grayfabric in the form of weave 4 by knitting in the same condition as inExample 1 except that the polyethylene terephthalate drawn yarn with 84dtex-48 f (filament) of Reference Example 3 was supplied to L1 (groundweave), L3, and L4.

Weave 4, Weave of Group a

L1: 84 dtex-48 f (PET drawn yarn), 1-2/1-0 (threading: full set)

L2: 84 dtex-36 f (PET false-twisted yarn), 3-4/1-0 (threading: full set)

L3: 84 dtex-48 f (PET drawn yarn), 2-3/2-1 1-0/1-2 (threading: a threadis alternately pushed in and pulled out)

L4: 84 dtex-48 f (PET drawn yarn), 1-0/1-2 2-3/2-1 (threading: a threadis alternately pushed in and pulled out)

Next, the knitted fabric was dyed in the same manner as in Example 1,and a hygroscopic polymer was fixed to the fabric, giving a fiberstructure of Example 4 having a weight per unit area of 318 g/m², afixing ratio of the hygroscopic polymer of 7.0%, a moisture absorptionratio of the fabric of 2.3%, and a moisture absorption ratio of thehygroscopic polymer of 32.8%. The fiber structure was cut in a directionperpendicular to the knitting direction, and the cross-section wasobserved under an electron microscope. The observation result indicatedthat the number of cross section fibers contained in the front layer was245, the number of cross section fibers contained in the back layer was854, and the ratio of the numbers of cross section fibers was 3.49.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 2.0° C., the coolness during sitting was“very good”, the texture was “good”, the light fastness was class 4, andthe fabric provided a comfortable feeling when a person sit.

Example 5

A 28-gauge tricot machine and three reeds were used to prepare a grayfabric in the form of weave 5 by knitting in the same condition as inExample 3 except that the polyethylene terephthalate drawn yarn with 84dtex-48 f (filament) of Reference Example 3 was supplied to L1 (groundweave) and L2 (ground weave).

Weave 5, Group a

L1: 84 dtex-48 f (PET drawn yarn), 2-3/1-0 (threading: full set)

L2: 84 dtex-48 f (PET drawn yarn), 1-0/1-2 (threading: full set)

L3: 84 dtex-36 f (PET false-twisted yarn), 1-0/3-4 (threading: full set)

Next, the knitted fabric was dyed in the same manner as in Example 1 andthen was raised with a raising machine. A hygroscopic polymer was fixedto the raised fabric in the same manner as in Example 1, giving a fiberstructure of Example 5 having a weight per unit area of 340 g/m², afixing ratio of the hygroscopic polymer of 12.6%, a moisture absorptionratio of the fabric of 2.9%, and a moisture absorption ratio of thehygroscopic polymer of 23.0%. The fiber structure was cut in a directionperpendicular to the knitting direction, and the cross-section wasobserved under an electron microscope. The observation result indicatedthat the number of cross section fibers contained in the front layer was231, the number of cross section fibers contained in the back layer was1,417, and the ratio of the numbers of cross section fibers was 6.13.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 2.4° C., the coolness during sitting was“very good”, the texture was “good”, the light fastness was class 4, andthe fabric provided a comfortable feeling when a person sit.

Example 6

A 28-gauge interlock circular knitting machine was used. Polyethyleneterephthalate false-twisted yarn with 84 dtex-72f (filament) wassupplied to the back fabric (ground weave), the polyethyleneterephthalate false-twisted yarn with 84 dtex-36 f (filament) ofReference Example 2 was supplied to the front fabric, and the yarns wereknitted at a course density on the machine of 38 course/2.54 cm toprepare a gray fabric where the front fabric was a patterned weave andthe back fabric was a plain knitted weave. The knitted fabric had astructure of group b.

Next, the knitted fabric was dyed in the same manner as in Example 1,and then a hygroscopic polymer was fixed to the fabric, giving a fiberstructure of Example 6 having a weight per unit area of 232 g/m², afixing ratio of the hygroscopic polymer of 8.6%, a moisture absorptionratio of the fabric of 2.0%, and a moisture absorption ratio of thehygroscopic polymer of 23.2%. The fiber structure was cut in a directionperpendicular to the knitting direction, and the cross-section wasobserved under an electron microscope. The observation result indicatedthat the number of cross section fibers contained in the front layer was161, the number of cross section fibers contained in the back layer was322, and the ratio of the numbers of cross section fibers was 2.00.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 2.6° C., the coolness during sitting was“very good”, the texture was “good”, the light fastness was class 4, andthe fabric provided a comfortable feeling when a person sit.

Example 7

Polyethylene terephthalate drawn yarn with 167 dtex-72f (filament) wasused as the warp and the weft to yield a double-woven fabric having aweave density of the warp of 250/cm and a weft weave density of the weftof 220/cm in both the ground weave and the pile.

The obtained woven fabric was dyed in the same condition as in Example 1and then was sheared with a shearing machine to give a pile length of1.8 mm, yielding a velvet fabric. A hygroscopic polymer was then fixedto the fabric in the same manner as in Example 1, giving a fiberstructure of Example 7 having a fixing ratio of the hygroscopic polymerof 10.5%, a moisture absorption ratio of the fabric of 3.5%, and amoisture absorption ratio of the hygroscopic polymer of 33.3%. The wovenfabric had a structure of group c.

The fiber structure was cut in a direction perpendicular to the weavingdirection, and the cross-section was observed under an electronmicroscope. The observation result indicated that the number of crosssection fibers contained in the front layer was 230, the number of crosssection fibers contained in the back layer was 980, and the ratio of thenumbers of cross section fibers was 4.26.

Table 1 shows the result of the performance evaluation. The knittedfabric had a surface temperature drop of 2.3° C., the coolness duringsitting was “very good”, the texture was “very good”, the light fastnesswas class 4, and the woven fabric provided a comfortable feeling when aperson sit.

Comparative Example 1

The weaves for the front fabric and the back fabric in Example 6 wasexchanged, that is, a 28 gauge interlock circular knitting machine wasused, the polyethylene terephthalate false-twisted yarn with 84 dtex-72f(filament) was supplied to the front fabric, the polyethyleneterephthalate false-twisted yarn with 84 dtex-36 f (filament) ofReference Example 2 was supplied to the back fabric (ground weave), andthe yarns were knitted at a course density on the machine of 38course/2.54 cm to prepare a gray fabric where the front fabric was aplain knitted weave the back fabric was a patterned weave.

Next, the knitted fabric was dyed in the same manner as in Example 1,and then a hygroscopic polymer was fixed to the fabric, giving a fiberstructure of Comparative Example 1 having a weight per unit area of 232g/m², a fixing ratio of the hygroscopic polymer of 8.6%, a moistureabsorption ratio of the fabric of 2.0%, and a moisture absorption ratioof the hygroscopic polymer of 23.2%.

The fiber structure was cut in a direction perpendicular to the knittingdirection, and the cross-section was observed under an electronmicroscope. FIG. 4 is the electron micrograph (×50). The observationresult indicated that the number of cross section fibers contained inthe front layer was 319, the number of cross section fibers contained inthe back layer was 162, and the ratio of the number of cross sectionfibers contained in the back layer/the number of cross section fiberscontained in the front layer (the ratio of the numbers of cross sectionfibers) was 0.51. The result also revealed that the hygroscopic polymerwas fixed to the ground weave of the knitted fabric.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 0.5° C., the coolness during sitting was“poor”, the texture was “good”, the light fastness was class 4, and thefabric provided a poor comfortable feeling when a person sit.

Comparative Example 2

A water jet loom-weaving machine was used, and the polyethyleneterephthalate false-twisted yarn with 167 dtex-48 f (filament) ofReference Example 2 was supplied as the warp and the weft to weave atwill weave having a weave density of warp of 128/2.54 cm and a weavedensity of weft of 81/2.54 cm.

Next, the woven fabric was dyed in the same manner as in Example 1, anda hygroscopic polymer was fixed, giving a fiber structure of ComparativeExample 2 having a weight per unit area of 197 g/m², a fixing ratio ofthe hygroscopic polymer of 8.3%, a moisture absorption ratio of thefabric of 1.9%, and a moisture absorption ratio of the hygroscopicpolymer of 22.8%.

The fiber structure was cut in a direction perpendicular to the weavingdirection, and the cross-section was observed under an electronmicroscope. FIG. 5 is the electron micrograph (×150). The observationresult indicated that the number of cross section fibers contained inthe front layer was 107, the number of cross section fibers contained inthe back layer was 133, and the ratio of the numbers of cross sectionfibers was 1.24. The hygroscopic polymer was fixed to the ground weaveof the woven fabric.

Table 1 shows the result of the performance evaluation. The fabric had asurface temperature drop of 1.3° C., the coolness during sitting was“poor”, the texture was “good”, the light fastness was class 4, and thefabric provided a poor comfortable feeling when a person sit.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 3 Example 4Example 5 Example 6 Example 7 Example 1 Example 2 Fabric Warp Warp WarpWarp Warp Circular Woven Circular Woven knitting knitting knittingknitting knitting knitting fabric knitting fabric Tricot Tricot RaisedTricot Raised Twill tricot tricot Composition Weight per 310 275 330 318340 232 400 232 197 unit area (g/m²) Thickness 0.73 0.67 1.01 0.74 1.050.6 3.0 0.60 0.42 (mm) Course (C) 59 50 60 59 60 39 (warp) 150 37 (warp)140 Wale (W) 33 33 40 33 40 37 (weft) 150 39 (weft) 96 Original L184T-48F- 167T-48F- 84T-48F- 84T-48F- 84T-48F- (back 167T- (back layer(warp) yarn drawn finished drawn drawn drawn layer 72F- side) 84T-167T-48F yarn yarn yarn yarn yarn side) drawn 36F 84T-72F yarn L284T-36F- 84T-36F- 84T-48F- 84T-36F- 84T-48F- (front — (back layer (weft)finished drawn drawn finished drawn layer side) 84T- 167T-48F yarn yarnyarn yarn yarn side) 72F 84T-36F L3 84T-48F- 84T-36F- 84T-48F- 84T-48F-84T-48F- — — — — drawn drawn finished drawn finished yarn yarn yarn yarnyarn L4 84T-48F- — — 84T-48F- — — — — — drawn drawn yarn yarn Weave L11-2/1-0 1-0/3-4 2-3/1-0 1-2/1-0 2-3/1-0 — — — — L2 3-4/1-0 2-3/2-11-0/1-2 3-4/1-0 1-0/1-2 — — — — 1-0/1-2 L3 2-3/2-1 1-0/1-2 1-0/3-42-3/2-1 1-0/3-4 — — — — 1-0/1-2 2-3/2-1 1-0/1-2 L4 1-0/1-2 — — 1-0/1-2 —— — — — 2-3/2-1 2-3/2-1 Number of 235 121 220 245 231 161 230 319 107cross section fibers contained in front layer Number of 850 485 1380 8541417 322 980 162 133 Cross section fibers contained in back layer Ratioof 3.62 4.01 6.27 3.49 6.13 2.00 4.26 0.51 1.24 numbers of cross sectionfibers (back layer/front layer) Performance Fixing ratio 7.3 12.3 12.57.0 12.6 8.6 10.5 8.6 8.3 of hygroscopic polymer (%) Moisture 2.4 3.03.0 2.3 2.9 2.0 3.5 2.0 1.9 absorption ratio of fabric (%) Moisture 32.824.3 24.0 32.8 23.0 23.2 33.3 23.2 22.8 absorption ratio of hygroscopicpolymer (%) Surface 2.1 1.9 2.3 2.0 2.4 2.6 2.3 0.5 1.3 temperature dropof fabric (° C.) Coolness Very Very Very Very Very Very Very Poor Poorduring good good good good good good good sitting Texture Very Very VeryGood (18 Good (22 Good (18 Very Good (20 Good (19 good (26 good (25 good(29 points) points) points) good points) points) points) points) points)(26 points) Light Class 4 Class 4 Class 4 Class 4 Class 4 Class 4 Class4 Class 4 Class 4 fastness

1. A fiber structure prepared by fixing a hygroscopic polymer to fibersof a fabric, a front layer on a front surface side of the fiberstructure and a back layer on a back surface side of the fiber structurehaving different fiber densities, a boundary between the front layer andthe back layer being on a center line of a cross section of the fiberstructure.
 2. The fiber structure according to claim 1, wherein thefabric is in the form of a woven fabric or a knitted fabric, and thefabric has a ground weave in the back layer side.
 3. The fiber structureaccording to claim 1, wherein the hygroscopic polymer is a polymer ofone or more monomers selected from sodium acrylamido-2-propanesulfonate,sodium styrenesulfonate, sodium isoprenesulfonate, sodiumallylsulfonate, and sodium methallylsulfonate or a copolymer of one ormore of the monomers and an additional monomer except the monomers. 4.The fiber structure according to claim 1, wherein the hygroscopicpolymer is fixed to the fabric in a fixing ratio of 4 to 20% by mass. 5.The fiber structure according to claim 1, wherein the number of crosssection fibers contained in the back layer divided by the number ofcross section fibers contained in the front layer (the ratio of thenumbers of cross section fibers) ranges from 2 to 10, where the fiberstructure is cut in the direction perpendicular to a weaving or knittingdirection of the fiber structure, and the center line of the crosssection is the boundary between the front layer on the front surfaceside and the back layer on the back surface side.
 6. The fiber structureaccording to claim 1, wherein the fabric has a weave selected from thefollowing groups a to c: group a: a warp knit that is produced with aknitting machine equipped with two or more reeds and has a two needleswing weave or a three needle swing weave for the back layer; group b: aweft knit that is produced with an interlock knitting machine and has apatterned weave for the front layer; and group c: a pile fabric having aground weave.
 7. A vehicle interior material comprising the fiberstructure according to claim 1.